The present invention relates to a rotary threaded fastener of the self-drilling and threading type and more particularly to a fastener which is manufactured by a pair of forging dies.
Self-drilling and thread forming fasteners are well known in the art. Some of these fasteners are particularly adopted for manufacturer by a milling process, others for manufacture by a forging process which employs a pair of matched dies, and some are susceptible to manufacture by either process. A typical example of a type of drilling and thread forming fastener which is preferably formed by the forging process is shown in U.S. Pat. No. 3,395,603, issued Aug. 6, 1968 to E. J. Skierski and assigned to the assignee of the present invention. Fasteners manufactured in accordance with the teachings of the aforementioned patent have met with wide acceptance as they provide a fastener which is simple to use, requiring no pre-drilling of the structure to which it is assembled, and these fasteners have proven to be easy to manufacture by mass production techniques.
As the use of these self-drilling and thread forming fasteners has increased, the requirement for the reduction in drilling time of the fastener has become important, particularly in those instances such as automobile manufacture, metal building construction, etc. where a large number of these fasteners are employed, and in particular, where mass production lines are employed to produce the product. In developing an improved threaded fastener of the self-drilling and threading type, therefore, a decrease in drilling time has become an ever important factor in the design.
It is therefore an object of the present invention to provide a drilling and thread forming fastener which exhibits a decrease in drilling time over those drilling and thread forming fasteners of the prior art.
It is a further object of the present invention to provide a drilling and thread forming fastener wherein the fastener exhibits an improvement in drilling time, particularly in the initial stages of the drilling.
Yet another object of the invention is to provide a drilling and thread forming fastener which exhibits an overall improvement in performance over those drilling and thread forming fasteners of the prior art.